Japanese Laid-open Patent Application No. 2007-25272 discloses an optical DVI cable system, which is called “a cable provided with an optical module” in the present application, used for transmitting digital signals, e.g., from a personal computer to a display apparatus. In the optical DVI cable system, a plurality of signals (e.g., R, G, and B signals) are converted from an electrical signal to an optical signal in a DVI connector located at the end of the cable.